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<title>Problem 2292. -- 【POJ Challenge 】永远挑战 -- 衡阳八中OJ离线版-2012-02-29</title><center><h2>2292: 【POJ Challenge 】永远挑战</h2><span class=green>Time Limit: </span>10 Sec&nbsp;&nbsp;<span class=green>Memory Limit: </span>128 MB<br><span class=green>Submit: </span>401&nbsp;&nbsp;<span class=green>Solved: </span>144<br>[<a href='submitpage.php?id=2292'>Submit</a>][<a href='problemstatus.php?id=2292'>Status</a>][<a href='bbs.php?id=2292'>Discuss</a>]</center><h2>Description</h2><div class=content><p>
<dd>
<div>
<p>lqp18_31和1tthinking经常出题来虐ftiasch。有一天, lqp18_31搞了一个有向图,每条边的长度都是1。 他想让ftiasch求出点1到点 <em>N</em> 的最短路。&quot;水题啊。&quot;, ftiasch这么说道。</p>
<p>所以1tthinking把某些边的长度增加了1（也就是说，每条边的长度不是1就是2）。现在，可怜的ftiasch要向你求助了。</p>
<p><img src="http://media.openjudge.cn/images/g3202_1.png" alt="" /></p>
</div>
</dd>
</p></div><h2>Input</h2><div class=content><p>
<dt>&nbsp; </dt>
<dd>
<div>
<p>第1行，两个整数 <em>N</em> (1 &le; <em>N</em> &le; 10<sup>5</sup>) 和 <em>M</em> (1 &le; <em>M</em> &le; 10<sup>6</sup>), 点和边的数量。</p>
<p>第2到 <em>M</em> + 1行: 三个整数 <em>U<sub>i</sub></em>, <em>V<sub>i</sub></em>, <em>W<sub>i</sub></em> (1 &le; <em>W<sub>i</sub></em> &le; 2), 从点 <em>U<sub>i</sub></em> 到 <em>V<sub>i</sub></em> 长度为 <em>W<sub>i</sub></em> 的边。</p>
</div>
</dd>
</p></div><h2>Output</h2><div class=content><p>
<dt>&nbsp; </dt>
<dd>
<p>一个整数，表示点1到点N的最短路。数据保证至少存在一条路径。</p>
</dd>
</p></div><h2>Sample Input</h2>
			<div class=content><span class=sampledata> <br />
3 3<br />
1 2 1<br />
2 3 1<br />
1 3 2<br />
</span></div><h2>Sample Output</h2>
			<div class=content><span class=sampledata>2<br />
</span></div><h2>HINT</h2>
			<div class=content><p></p></div><h2>Source</h2>
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